1. Field of the Invention
This invention relates generally to devices and methods for determining the blood alcohol concentration of a person. More particularly, the invention relates to a device and method for determining the blood alcohol concentration of a machine operator prior to or during operation of the machine.
2. Description of Related Art
Various techniques have been employed for calculating a person's blood alcohol concentration by measuring breath samples. In a first method, the alcohol content in a breath sample is measured using a semiconductor sensor commonly referred to as a Taguchi cell. This method typically provides a low cost device, but instruments incorporating the Taguchi cell sometimes demonstrate poor accuracy.
A second method employs an infrared absorption technique for determining the blood alcohol concentration. This method has proven to have very high accuracy levels, but the sensor systems incorporating this technique are sometimes more expensive than other methods.
A third method employs a fuel cell together with an electronic circuit. The fuel cell method is described in U.S. Pat. No. 4,487,055, which is hereby incorporated by reference. Although this method typically provides more accuracy than the Taguchi cell, the systems comprising this method can be relatively expensive. One reason for the high cost associated with fuel cell techniques is that the method requires that a breath sample be of a determinable volume. Historically, this has been accomplished through the use positive displacement components such as piston-cylinder or diaphragm mechanisms. A more recent advance in the use of fuel cell sobriety devices is described in U.S. Pat. Nos. 6,026,674 and 6,167,746, which are hereby incorporated by reference. These devices provide an electronically controlled valve that selectively regulates the volume of air that passes through the fuel cell.
Sobriety detection systems have enjoyed increasing popularity in sobriety interlock systems for vehicles and other machinery. Sobriety interlock systems are wired into the ignition circuits of vehicles to prevent an operator from operating the vehicle while intoxicated. Until the operator can provide a breath sample that is either alcohol free or below a certain level, the sobriety interlock prevents operation of the vehicle. Some sobriety interlocks even attempt to log vehicle data such as vehicle speed, mileage, and time of operation. This data can be used to provide progress reports and evidentiary reports to authorities monitoring the activities of operators who have been criminally convicted of operating vehicles under the influence of alcohol.
The primary problem with existing sobriety interlock systems is the difficulty by which information is gathered from the vehicle to which the devices are attached. To obtain information about whether the engine of the vehicle is on, the interlock system must be connected directly to the ignition system. To determine the speed of the vehicle at any particular time, either a speed sensor must be installed, or the interlock device must be hard-wired to the vehicle's speedometer. Another circuit must be wired from the interlock system to a mileage sensor to determine how far the vehicle has traveled. This data as well as other data related to the operation of the vehicle is critical to the interlock system's logging function, however, the installation of individual circuits connected to the interlock system and sensors located throughout the vehicle makes comprehensive monitoring and logging of the vehicle's operating parameters difficult, if not impossible.
Another related problem with existing interlock systems is the difficulty in providing secure electrical connections between the interlock system and the vehicle. Electrical connections should preferably be secure and tamper-proof, so that data received by the interlock system cannot be altered or manipulated. Since multiple electrical connections are usually required with existing systems, each connection must be separately secured, thereby increasing the time and costs of installation.
A need exists, therefore, for a sobriety interlock device that is capable of quickly and efficiently obtaining operating parameters from a machine to which the sobriety interlock device is connected. A need also exists for a sobriety interlock device that is easy to install on the machine, and that requires a smaller number of separate electrical connections between the interlock system and the machine.